1. Field of the Invention
The present invention generally relates to a drive device. More specifically, the present invention relates to a drive device used in an image forming device.
2. Background Information
Image forming devices such as color printers, color copiers, and the like, have rotation drive devices to rotate and to drive an image forming unit, e.g. photosensitive drums for each color component, transfer belts, and so on. Some rotation drive devices include a motor and a planetary speed reduction device to reduce the speed of the motor.
In recent years, with the reduction in cost of image forming devices there is a tendency to form at least part of the planetary roller in the planetary speed reduction device using an elastic material such as, for example, rubber. Elastic deformations are produced in planetary rollers made from an elastic material because the planetary rollers are pressed against the output shaft to transmit the rotation of a motor to the outside. The elastic deformations of the elastic material of the planetary roller cause a change in the rotation speed of the output shaft of the speed reduction device. Furthermore, color distortion, color unevenness, and the like appears in the images produced when the rotation speed of the output shaft of the speed reduction device fluctuates.
In Japanese Patent Application Laid-open No. 2002-171779, a rotation drive device is disclosed in which when an elastic material is used in the planetary roller, the rotation speed of the motor is directly controlled to obtain a uniform rotation speed of the output shaft. Specifically, the rotation drive device of Japanese Patent Application Laid-open No. 2002-171779 includes a stepping motor, an elastic material speed reduction device, and a feedback control unit. The elastic material speed reduction device includes a torque transmission unit that transmits torque by frictional contact of the elastic material, and does not include a torque transmission unit that uses gears. The elastic material speed reduction device reduces the rotation speed of the motor and outputs the rotation speed to the photosensitive drum. The feedback control unit measures the output rotation speed of the elastic material speed reduction device, obtains the difference from the standard speed, and applies a speed command signal to the motor based on the value of the difference so that the rotation speed of the motor is directly controlled.
However, the device of Japanese Patent Application Laid-open No. 2002-171779 has the following problem points.
The elastic deformation occurs in the elastic material of the planetary roller during the time that motor rotation has stopped until the motor is driven again. This deformation causes non-uniformity in the rotation speed of the output shaft of the speed reduction device for a while after starting to drive again. The period of time that the rotation speed of the output shaft of the speed reduction device is non-uniform as a result of elastic deformation induced in the planetary roller when the motor is stopped is much longer than the response time of the feedback control of the device in Japanese Patent Application Laid-open No. 2002-171779. Therefore, detecting non-uniformity of the rotation speed of the output shaft of the speed reduction device caused by elastic deformation of the planetary roller when the motor is stopped and controlling the rotation speed by the feedback control of the device of Japanese Patent Application Laid-open No. 2002-171779 will result in over-control.
Further, the time required until the elastic deformation in the elastic material of the planetary roller recovers as a result of the rotation of the motor depends on the temperature of the planetary roller. For example, if the planetary roller is at a low temperature, the time required until the elastic deformation of the planetary roller recovers becomes longer. The temperature of the planetary roller varies depending on the environment in which the color image forming device is used.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a drive device used in an image forming device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.